1. Field of the Invention
This invention relates to a process for aerobically biodegrading oily sludges.
2. Description of the Prior Art
Historically, land farming has been widely used for the biodegradation and disposal of organic wastes and oily sludges. Land farming involves applying the waste to soil and tilling the waste into the soil to allow aerobic bacteria to convert the organic components into carbon dioxide, water and humic matter. Periodic tilling of the soil is necessary to mix the waste uniformly into the soil and to allow air to reach the bacteria and promote the reaction. The availability of the land farming technique has been sharply reduced as a result of regulations relating to the land disposal restriction for hazardous wastes and the environmental impact of the process. In particular, odor generation, the deposition of heavy metals in the soil, and the potential contamination of ground water supplies have resulted in a major reduction in the use of land farming for treating organic and oily wastes.
In many places, composting has taken the place of land farming. Composting is a thermophilic biological process that is widely used for the treatment of municipal sludge and other organic wastes. An important aspect of composting is that the process can be conducted under controlled conditions, thus avoiding the problems inherent in open land farming. A significant use of composting relates to the treatment of municipal sludge. This process is often done by mixing the municipal sludge with a bulking agent, removing excess free water, and subjecting the mixture to forced aeration at an elevated temperature to speed up the composting process. In general, municipal sludge, as well as other types of organic waste, together contain both active microorganisms and nutrients which can initiate and maintain the biological conversion process under suitable conditions.
Oily sludge is extensively found in oil refineries and is also generated in a range of manufacturing operations. In refineries, the oily sludge is produced in a variety of clarifier processes, in holding tanks, and in settling ponds for liquid waste. In general, oily sludge is characterized as relatively low in solids content and which exhibits little biological activity. This latter property is primarily due to the deficient nutrient and electron acceptor contents of the oily sludge.